Hypertrophic cardiomyopathy (HCM), is a hereditary disease that is an important cause of sudden death (SD), particularly in the young. When complicated by obstruction to left ventricular outflow tract (LVOT) it is frequently associated with dyspnea, palpitations, lightheadedness, and syncope. In the past year, progress was made in the following areas: 1) identification of HCM pts who are at risk for SD and syncope; 2) establishment of myocardial ischemia as the most important mechanism of SD and syncope in children with HCM; 3) antiarrhythmic therapy for ventricular tachycardia (VT) in patients at high risk for SD; 4) evaluation of dual chamber (DDD) pacing as an alternative to cardiac surgery for relief of LVOT obstruction; and 5) obtain a better understanding of the genetics of the disease. A study of 225 pts (follow up, 3 years), revealed that 1) non-sustained VT on Holter is of benign prognostic significance in pts without symptoms of impaired consciousness, and who do not have VT induced at electrophysiologic study, and 2) inducibility of VT, especially when associated with syncope or cardiac arrest, identifies a subgroup of pts at high risk for SD. In a study involving 54 young pts, myocardial ischemia was the sole cause of syncope/cardiac arrest in pts aged <14 yrs. UK68798, a novel class III drug, was found to have potent antiarrhythmic properties in HCM: VT could no longer be induced or was more difficult to induce in 13 pts. DDD pacing was found to improve symptoms and exercise performance associated with reduction in LVOT obstruction in 21/24 pts with drug-refractory symptoms. Normal echocardiograms recorded in pts who were obligate carriers of HCM by virtue of their position in the pedigree established the occurrence of generational 'skips'. Children of two families in which disease gene maps to chromosome 14 but who have normal cardiac morphology are being evaluated. Syncope due to bradycardia in an otherwise normal 9-mth child suggest that HCM may cause sudden infant death syndrome (SID).